(1) Field of the Invention
The present invention relates to regulated power supplies and more particularly to a switching regulated, pulse width modulated, push-pull converter.
(2) Description of the Prior Art
Current state-of-the-art switching regulated, push-pull converter circuits have good reliability, stability and performance. However, to achieve these characteristics such converters must meet the following criteria: (1) provide symmetrical primary volt-second balance to keep the transformer of the converter operating in the center of its linear region, (2) prevent overlap of the switching intervals during which both switching transistors are operating, and (3) prevent each switching transistor from switching excessive current levels due to an output voltage overload or a voltage spike on the input voltage source.
The typical prior art methods of solving these problems are to include a current sensing means in the output circuit to respond to overload conditions.
Overlap is usually prevented through the use of a transformer proportional drive circuit where their switching transistors are prevented from going into deep saturation keeping storage and fall times to within limits of set guard bands, all at the expense of high DC transistor losses.
Primary volt-second balance schemes range from sensing out feedback of transformer flux to providing always matched pairs of time equal drive pulses.
Accordingly, it is an object of the present invention to provide symmetrical primary volt-second balance, prevent transistor switching overlap and protect the switching transistors from excessive current demands without sacrificing DC losses or high saturation voltages.
Another problem with prior art multiple output converters is the primary load requirement for the converters. These circuits all require a minimum load on the primary output before the auxiliary output can function.
Accordingly it is a further object of the present invention to solve the minimum load dilemma of multiple output switching converters.